The present application is based on Japanese Patent Application No. 2000-157713, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a laminated optical device which can control optical properties such as polarization, phase, scatter, and reflection, and which is excellent in reduction in thickness and weight, and a liquid-crystal display device using the laminated optical device.
2. Description of the Related Art
There has been heretofore used a method in which optical members such as a polarizer, a retardation compensating birefringent plate, and a luminance-enhancing film for use in assembling of a liquid-crystal display apparatus or the like are formed separately so that these optical members can be laminated to produce the liquid-crystal display apparatus or the like as occasion demands. Incidentally, the birefringent plate is provided for improving display quality by optically compensating for the birefringent anisotropy of liquid crystal. In liquid crystal in a twisted nematic mode, or a vertical or horizontal alignment mode, the birefringent plate is used for widening the viewing angle. In this case, a plurality of birefringent plates are often used for liquid crystal in a reflection type twisted nematic mode to improve display quality.
In the method of laminating optical members formed separately, there was, however, a problem that increase in thickness and volume was inevitable because interposition of an adhesive layer such as an adhesive layer was required for the lamination. Incidentally, there have been proposed a laminate of a plurality of birefringent plates and a polarizer (Japanese Patent Publication No. 5-27118 and Japanese Patent Publication No. 5-100114), a laminate of a luminance-enhancing film, a quarter-wave plate and a polarizer (Japanese Patent Publication No. 9-189811), and a laminate obtained by bonding and laminating optical members (WV film made by Fiji Photo Film Co., Ltd. and DBEF made by 3M Company) obtained by providing obliquely oriented liquid-crystal polymer layers on the laminates as listed above.
In the laminate, however, the thickness of each of optical members such as a polarizer and a birefringent plate is generally in a range of from 20 to 300 xcexcm. For this reason, in some case, the total thickness of the laminate exceeds 700 xcexcm. Hence, there was a problem that the liquid-crystal display apparatus became remarkably bulky. In addition, there was a disadvantage that weight was increased too much and increase in size of the liquid-crystal display screen was difficult to be achieved.
An object of the present invention is to develop a laminated optical device which has a plurality of optical functions such as a polarizing function and an optically compensating function and which is excellent in reduction in thickness and weight.
The Invention provides a laminated optical device formed of a laminate having a polarizing layer having a thickness of not larger than 5 xcexcm, and at least one birefringent layer including either a solid film of oriented liquid crystal or a polymer layer containing oriented liquid crystal. Accordingly, the invention provides a liquid-crystal display apparatus having: a liquid-crystal display panel; and at least one laminated optical device defined above and disposed on one of opposite surfaces of the liquid-crystal display panel.
According to the invention, a birefringent layer made of oriented liquid crystal can be formed on a polarizing layer through an oriented film in accordance with necessity so that the birefringent layer is superposed closely on the polarizing layer. Thus, a laminated optical device can be obtained. The polarizing layer is excellent in reduction in thickness so that the laminated optical device is excellent in reduction in thickness and weight as a whole. The laminated optical device exhibits a plurality of optical functions such as a polarizing function based on the polarizing layer, and an optically compensating function and/or a luminance enhancing function based on the birefringent layer.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with attached drawings.